Epidemiology

Occupational asthma is most common type of occupational lung disease in industrialized countries

Occupational asthma accounts for 26% of all occupational lung disease cases in UK SWORD data, 52% of cases in British Columbia (due to high rates of western red cedar exposure), and 15% of cases in US (according to 1978 Social Security data)

Occupational exposures cause between 8-21% of “asthma”/wheezing cases in population (depends on definition of “asthma” and definition of exposure)

Atopy/Smoking: these are NOT risk factors for the development of occupational asthma due to diisoocyanates and western red cedar

Genetic Risk Factors: HLA associations (both associated with and protective) have been described for occupational asthma due to platinum, acid anhydrides, western red cedar, diisocyanates, soybeans, and latex

High MW Compounds:

IgE-mediated (complete allergens, do not require interaction with any proteins): animal, plant, and bacterial proteins

Methacholine Challenge: may be useful in cases with normal spirometry
–Best Test for Airway Reactivity: a negative methacholine challenge within 2 weeks of the last exposure makes occupational asthma very unlikely

Peak Flow: may be useful, if measured QID and log is kept
-A >20% diurnal variation in peak flow rates is suggestive, but a work-related pattern of decrease is probably the best criteria

Some concern about peak flow rates being too dependent on patient effort, but most believe them to have adequate sensitivity/specificity for the diagnosis of occupational asthma

Bronchial Provocation Studies: rarely performed in US

Quebec studies indicate that these can be performed safely, if conducted in a controlled, monitored setting

Skin Testing: useful to test for presence of atopy (which is a risk factor for high MW sensitizer-associated asthma)

Extracts Available For: flour, animal proteins, coffee

IgE Antibodies: can be used to test for high MW sensitizers and some low MW sensitizers (like diisocyanates and acid anhydrides)

Anti-Toluene Diisocyanate IgE (by RAST): present in only 15-18% of cases (and signifiies only sensitization, but does not establish it as a cause of the occupational asthma)

Not commercially available

CXR/Chest CT Patterns

Hyperinflation/flattening of diaphragms, bronchial wall thickening, mucus plugging, and fleeting infiltrates: may been seen during an exacerbation

With High MW substances: rhinoconjunctivitis occurs prior to development of respiratory symptoms (possible due to high MW substances invoking an IgE-mediated immune response)

Pattern of Symptoms

Pattern of presentation in association with work is the best diagnostic feature (since many chemicals that cause occupational asthma have not been specifically identified and multiple causative agents may be simultaneously present)

History is also useful to rule out an occupational cause, if one is not present

Occasionally, a single exposure to an offending agent may result in repeated asthmatic reactions over several days

Latency Period: in sensitizer-induced cases, symptoms usually do not develop immediately, but develop after some period of occupational exposure

Typical Latency for Platinum-Associated Occupational Asthma: around 17 days

Typical Latency for Toluene Diisocyanate-Associated Occupational Asthma: around 2 years

Typical Latency for Baker’s Occupational Asthma: around 4.2 years

Relationship of Symptoms to Work

Symptoms that occur only at work

Symptoms that improve on weekends/vacations

Symptoms that occur regularly after the work shift (late asthmatic responses, 2-4 hrs later, may occur with some aeroallergens and toluene diisocyanate)

Symptoms that progressively increase over the course of the work week

Symptoms that improve after a change in work environment

ACCP 1995 Criteria

History compatible with occupational asthma

Presence of airflow limitation and its reversibility

In the absence of airflow limitation, presence of non-specific airway responsiveness

Demonstration of work-relatedness by objective means

NIOSH SENSOR Case-Classification Criteria

(work-related state-based surveillance program)

Work-Aggravated Asthma: pre-existing asthma that was symptomatic and/or treated with asthma medications within the 2 years prior to entering the occupational setting associated with the patient’s asthma symptoms

Reactive Airways Dysfunction Syndrome (RADS): new asthma symptoms that develop within 24 hrs after a one-time high level inhalation exposure (at work) to an irritant gas, fume, smoke, or vapor and that persist for at least 3 months

Classic/Work-Induced Asthma

Workplace exposure to an agent previously associated with occupational asthma

Limited data about extent and time-course of recovery after cessation of exposure

In a study of pulp mill workers who were acutely “gassed”, a majority had increased nonspecific airway hyperresponsiveness 2 years later

Standard Asthma Treatment

Inhaled steroids: shown to small, but significant, improvement in both low and high MW sensitizer-induced asthma (after withdrawal of exposure)

Better efficacy if used early, rather than late, in course of occupational asthma

Role on inhaled steroids in irritant-induced asthma is unclear

Prevention of Occupational Asthma

Primary prevention: prevent exposures

Ex: engineering control (process enclosure, respirators, etc.)

Secondary prevention: surveillance with early detection of asthma (so that duration and severity of asthma can be minimized)

Ex: paint-spraying industry (with exposure to diisocyanates)

Any case of occupational asthma should be considered a sentinel event: other at risk workers should also be screened (surveys, diurnal peak flows, spirometry, skin testing for high MW antigens, etc. by medical department) and exposure monitoring (air monitoring, etc. by industrial hygienists) should be instituted

Tertiary prevention: appropriate healthcare and prevention of further exposure in those who have already been diagnosed

Prognosis

Disability

Occupational asthma may result in significant long-term disability and unemployment

Rates of job loss and jon change are high

50% of patients have reduced income, when assessed 3 years after diagnosis is made

ATS Scoring system for disability (assessed when disease has been optimally treated and stabilized), includes these factors:

Post-bronchodilator FEV1

Reversibility of FEV1 or degree of non-specific airway responsiveness

Minimum asthma medication needed for optimum control

Hospitalization Rates

Occupational asthma patients have higher all-cause hospitalization rates, as compared to non-asthmatics (but have lower hospitalization rates than that of non-occupational asthma at tertiary care centers)